Lubiprostone, (−)-7-[(2R,4aR,5R,7aR)-2-difluoropentyl-2-hydroxy-6-oxo-octahydrocyclopenta[b]pyran-5-yl]heptanoic acid, is a kind of prostaglandin compounds, and usually exists in the following tautomeric forms:

Lubiprostone, a local activator of chloride channel, can specifically activate type II chloride channel on the cell membrane of a epidermal cell in the gastrointestinal tract, stimulate the secretion of intestinal fluid having a high chloride ion concentration, and enhance the intestinal motility so as to facilitate the softened feces to move along the intestinal tract and relief the conditions of constipation. Lubiprostone capsule (lubiprostone/Amitiza, by American Sucampo Pharmaceuticals) was approved by the US Food and Drug Administration (FDA) for the treatment of chronic idiopathic constipation in adults.
However, the lubiprostone prepared and used now is in an amorphous form, which has an oily appearance. It is difficult to control the purity and homogeneity of a medicament in the procedure for the preparation of the medicament when the compound is in an amorphous form. In addition, the stability of amorphous lubiprostone is not satisfactory.
No research or report was provided for lubiprostone crystal forms in the field. Therefore, it is an urgent need for developing lubiprostone crystal suitable for the preparation of corresponding medicament.